The regulation of the volume and composition of the body fluids is primarily dependent upon vasopressin (ADH, antidiuretic hormone), the renin-angiotensin-aldosterone system, and possibly a humoral natriuretic factor. Furthermore, the control of blood volume is an important factor in the regulation of arterial blood pressure. The primary objective of this research proposal is to delineate the role of ADH in these regulatory processes. The specific issues which will be examined are: the physiological role of the brain iso-renin-angiotensin system and brain prostaglandins in the control of ADH release from the neurohypophysis; the factors which affect the clearance of ADH from the circulating blood by the kidneys and liver; the role of the renal and hepatic clearances of ADH in the control of the plasma ADH concentration; and the study of the metabolic clearance of ADH with tritiated arginine vasopressin.